diff --git a/fimfarchive/mappers.py b/fimfarchive/mappers.py
index 341afbc..0fa4172 100644
--- a/fimfarchive/mappers.py
+++ b/fimfarchive/mappers.py
@@ -24,11 +24,12 @@ Mappers for Fimfarchive.
 
 import os
 from abc import abstractmethod
-from typing import Generic, Optional, TypeVar
+from typing import Dict, Generic, Optional, Set, TypeVar
 
 from arrow import api as arrow, Arrow
 
 from fimfarchive.exceptions import InvalidStoryError
+from fimfarchive.flavors import MetaFormat
 from fimfarchive.stories import Story
 
 
@@ -115,3 +116,24 @@ class StoryPathMapper(Mapper[str]):
         key = str(story.key)
 
         return os.path.join(directory, key)
+
+
+class MetaFormatMapper(Mapper[Optional[MetaFormat]]):
+    """
+    Guesses the meta format of stories.
+    """
+    spec: Dict[MetaFormat, Set[str]] = {
+        MetaFormat.ALPHA: {'likes', 'dislikes', 'words'},
+        MetaFormat.BETA: {'num_likes', 'num_dislikes', 'num_words'},
+    }
+
+    def __call__(self, story: Story) -> Optional[MetaFormat]:
+        items = self.spec.items()
+        meta = set(story.meta.keys())
+
+        matches = {fmt for fmt, spec in items if spec & meta}
+
+        if len(matches) == 1:
+            return next(iter(matches))
+        else:
+            return None
diff --git a/tests/test_mappers.py b/tests/test_mappers.py
index 9c5db5d..82b14d5 100644
--- a/tests/test_mappers.py
+++ b/tests/test_mappers.py
@@ -23,12 +23,16 @@ Mapper tests.
 
 
 import os
+from typing import no_type_check, Dict, Any
 from unittest.mock import patch, MagicMock, PropertyMock
 
 import pytest
 
 from fimfarchive.exceptions import InvalidStoryError
-from fimfarchive.mappers import StaticMapper, StoryDateMapper, StoryPathMapper
+from fimfarchive.flavors import MetaFormat
+from fimfarchive.mappers import (
+    MetaFormatMapper, StaticMapper, StoryDateMapper, StoryPathMapper
+)
 from fimfarchive.stories import Story
 
 
@@ -108,7 +112,7 @@ class TestStoryDateMapper:
         """
         Tests `None` is returned when meta contains no dates.
         """
-        meta = {
+        meta: Dict[str, Any] = {
             CHAPTERS: [
                 dict(),
                 dict(),
@@ -259,6 +263,7 @@ class TestStoryPathMapper:
 
         assert mapper(story) == path
 
+    @no_type_check
     def test_casts_values(self, tmpdir, story):
         """
         Tests casts all values to string when joining.
@@ -274,3 +279,58 @@ class TestStoryPathMapper:
         assert mapper(story) == os.path.join('dir', 'key')
         assert directory.__str__.called_once_with()
         assert story.key.__str__.called_once_with()
+
+
+class TestMetaFormatMapper:
+    """
+    MetaFormatMapper tests.
+    """
+
+    @pytest.fixture
+    def mapper(self):
+        """
+        Returns a meta format mapper instance.
+        """
+        return MetaFormatMapper()
+
+    @pytest.fixture(params=['likes', 'dislikes', 'words'])
+    def alpha(self, request):
+        """
+        Returns an alpha meta key.
+        """
+        return request.param
+
+    @pytest.fixture(params=['num_likes', 'num_dislikes', 'num_words'])
+    def beta(self, request):
+        """
+        Returns a beta meta key.
+        """
+        return request.param
+
+    def merge(self, story, *keys):
+        """
+        Returns a story containing the requested meta keys.
+        """
+        meta = {key: i for i, key in enumerate(keys, 1)}
+        return story.merge(meta=meta)
+
+    def test_alpha_format(self, mapper, story, alpha):
+        """
+        Tests alpha meta format is detected.
+        """
+        story = self.merge(story, alpha, 'misc')
+        assert mapper(story) == MetaFormat.ALPHA
+
+    def test_beta_format(self, mapper, story, beta):
+        """
+        Tests beta meta format is detected.
+        """
+        story = self.merge(story, beta, 'misc')
+        assert mapper(story) == MetaFormat.BETA
+
+    def test_conflict(self, mapper, story, alpha, beta):
+        """
+        Tests None is returned for conflicting meta keys.
+        """
+        story = self.merge(story, alpha, beta)
+        assert mapper(story) is None